1. Field of the Invention
The present invention relates to a method for manufacturing hydroxylamine, particularly a method using hydrogen gas as reducing agent to reduce the nitrate ions to produce hydroxylamine.
2. Description of Related Art
Hydroxylamine related manufacturing steps are generally combined with other manufacturing steps to constitute a recycling system in the industrial application, for example, hydroxylamine—oximation recycling system, i.e., using phosphate salt as an aqueous reaction medium, and using nitric acid, hydrogen gas as raw materials in a catalytic reaction to reduce nitrate ions to hydroxylamine, followed by adding cyclohexanone to the produced hydroxylamine to proceed the oximation reaction to form cyclohexanone oxime. After the foregoing oximation reaction, the resultant reaction mixture was supplemented with nitric acid or subjected to adsorption of nitrous gas to generate nitric acid in order to increase the required amount of nitrate ions, which were consequently transferred into a hydroxylamine reactor for the hydroxylamine synthesis. The reactions could be shown as follows:
Reaction of Hydroxylamine to Produce Hydroxylamine PhosphateNH4NO3+2H3PO4+3H2→NH3OH.H2PO4+NH4H2PO4+H2O
Oximation Reaction to Produce Cyclohexanone OximeNH3OH.H2PO4+C6H10O→C6H10NOH+H2O+H3PO4 
Supplementation of Nitrate Ion to the Inorganic Phosphate Manufacturing Solution.HNO3+H2PO4−→NO3−+H3PO4 
During the manufacturing process, the aqueous reaction medium was recycled through the hydroxylamine reaction zone and the cyclohexanone oxime synthesizing zone. The content and the quality level of the reaction medium directly affected the efficiency of the hydroxylamine production. U.S. Pat. No. 3,767,758 discloses that the aqueous reaction medium containing metals such as Mo, Rh and Ru declines the selection rate of the hydroxylamine production. U.S. Pat. No. 4,062,927 discloses that acidic solution corrupts the equipments and devices to increase the amount of heavy metal contamination in aqueous reaction medium, particularly, the generated Mo metal contamination may decline the selection rate by 5 to 15%. Said patent teaches the using of ferric ammonium phosphate as a precipitant to remove the metal ions in the reaction medium by co-precipitation. However, the selection rate of the hydroxylamine production is still lower than 87% according to the disclosure of said patents.
Therefore, a method in which the process is simple and effectively increasing the selection rate of the hydroxylamine production while maintaining high catalytic activity is indeed required.